A Snake?

Trivia
Trivia brain teasers have some element of trivia in them, but they are not just pure trivia questions.

John sat at a table reading a book. When his intelligent friend Jane came in, he casually adjusted his glasses lenses as they slid down his nose and glanced up at her. Suddenly, she burst out laughing.

John asked, "What is so funny?"

Jane answered, "You remind me of a snake!"

How did John remind Jane of a snake, when to most people John did not look, sound, or seem like a snake?

Hint

What is one of the things that makes snakes' vision different from people's vision?

Answer

Snakes adjust their vision by moving their eyes' lenses forward and backwards rather than bending them.